Unveiling Ion-Pairing and Anion Dual Charge Carrier in Ca-Organic Batteries.

Calcium-organic batteries offer sustainable energy storage with high voltage, yet their reaction mechanisms remain unclear. Here, a hidden dual-ion charge storage mechanism is unveiled in poly(anthraquinone imide) (PAQI) using Ca(TFSI)₂/ether-based electrolytes, challenging the conventional Ca⁺-only storage model. It is demonstrated that Ca⁺-TFSI⁻ ion pairs co-bind to carbonyl groups during the first electron transfer, followed by TFSI⁻ dissociation to activate adjacent carbonyl sites in the second step-a process reversible upon charging. This mechanism critically depends on electrolyte solvation structures: G4 (tetraglyme) uniquely stabilizes monodentate CaTFSI⁺ contact ion pairs (versus multidentate aggregates in [G1 (monoglyme)/G2 (diglyme)] due to its optimal Ca⁺ solvation energy, enabling exceptional performance. The PAQI/G4 system achieves a discharge capacity of 114 mAh g⁻¹ at 20 mA g⁻¹ and ultralong cycling (10 000 cycles with 94.5% capacity retention at 1000 mA g⁻¹), surpassing prior calcium-organic batteries at room temperature. This work redefines cation-anion interplay in organic electrodes and establishes electrolyte solvation engineering as a pivotal strategy for high-performance, durable calcium battery systems.